A physical model involving two different crystalline sites for dissolution has been proposed to explain the dissolution behavior of hydroxyapatite and tooth enamel. This model has been used to correlate the behavior of hydroxyapatite observed at the crystal level with behavior observed at a macro level, for example, a compressed pellet of hydroxyapatite or a block of tooth enamel. The object of this project is to extend the model so that is accurately describes remineralization as well as demineralization, including the effect that demineralization has on the rate and extent of subsequent remineralization. The experimental aspect of the project is focused on the kinetics of demineralization and remineralization of suspensions of hydroxyapatite crystals, considering the influence of both ambient solution composition (including the presence or absence of fluoride) and the current state of the crystals (demineralized, already partly remineralized or untreated). As a model for the behavior of suspensions evolves, this information will be used to build a model for the compressed pellet of hydroxyapatite and appropriate experiments will be done to test the model, incorporating demineralization/remineralization kinetics, fluoride gradients and mineral density gradients as the main observables. A successful model would contribute much to our quantitative understanding of the behavior of hydroxyapatite and enamel and would ultimately be a useful tool in the design of therapy for enhancing caries resistance or repairing early lesions.